Good tools are a must if you plan to do your own work on your car

A mechanic is only as good as the tools he uses! That's what they used to say about professional mechanics, but nowadays it applies to anyone who hopes to repair his car.

Using improper tools on today's complex cars can lead to hours of wasted time and torment. Also, the backyard mechanic had better know what he's getting into because the new cars of today aren't the much simpler cars of a few years ago.

A tool that doesn't grip properly can break, bend, or strip fastener such as nuts, bolts, and screws. The wrong tool also can slip under force, resulting in bruised knuckles to the car owner.

Conversely, the right tools can help you speed through repairs and do a more efficient job of replacing shocks, installing exhaust parts, changing oil, doing tuneups (if you know what you're doing), and performing a number of other jobs on the car.

But what tools do you need? How much should you spend? And where should you go to buy them?

Here are some ideas for an all-purpose tool kit that will help you do a good job of maintaining the family car:

* Standard screwdrivers, one with a 4-inch blade (1/8-inch tip) and one with a 6-inch blade (1/4-inch tip), plus a couple Phillips-head screwdrivers, one with a 3-inch blade and one with a 6-inch blade, are essential for removing the different kinds and sizes of screws which you'll encounter in even the simplest jobs such as changing car-registration plates and replacing headlamps and taillights.

Never use a wide blade on a small screw or a small blade on a large screw. You'll only damage the slot in the head of the screw that way.

* A handy choice of versatile pliers will save precious time on a variety of gripping jobs. Standard slip-joint pliers (adjustable to two widths) will handle many routine jobs and cut down on the time normally spent in reaching or shuffling about for a larger tool.

Needle-nose pliers will make fast work of pulling off and putting on electrical connections. With your fingers, you often waste time trying to fit the parts together. Vise-grip pliers (an adjustable plier that stays on when locked) is very handy for getting a firm grasp on fasteners while, simultaneously, freeing both hands to perform a secondary function that will speed along repairs.

* A set of open-and-closed-end combination wrenches in graduated sizes from 3 /8-inch to 7/8-inch will save time (and muscle) loosening and tightening hard-to-get-at fasteners in the engine compartment.

With pliers or most other wrenches you could labor here till Christmas, trying to get a good grip, reach, and leverage. For easily accessible bolts and nuts outside the engine, you'll save even more time by using a 6-inch adjustable jaw wrench which can handle most fasteners (up to 7/8-inch bolts) at the mere turn of a dial.

* A 3/8-inch drive socket-wrench set is indispensable for whizzing through the removal and replacement of spark plugs and bolts. With a wrench, you lose time getting a new grasp after each turn, and it takes more turns and exertion to get the job done.

Many socket sets are available, so read the package contents carefully for the one that has these items: 3-inch and 6-inch extensions; 6-point and 12-point sockets in graduated sizes from 3/8-inch to 7/8-inch (7 mm to 19 mm for metric bolts); 8-inch reversible ratchet; universal joint for working around tight areas; and a 13/16-inch spark-plug socket.

If you've planned some electrical work such as putting in a CB or radio, you'll also need a 1/4-inch adaptor and a 1/4-inch socket.

All of these tools vary greatly in price, depending on the brand and where you shop. In general, tools are usually most inexpensive if bought through a volume retail outlet, discount house, or chain store. Prices at auto parts store are normally higher, but these outlets generally carry the top brands and their personnel are more helpful in choosing the right tools for your needs.

Regardless of where you buy, keep these rules of thumb in mind: Always read the warranties and try to get the best-quality tools for the price you can afford. Cheap tools tend to wear fast and can even damage parts.

If you don't want to buy the tools or will only use them infrequently, try borrowing them from a neighbor or call one of the tool-rental outlets listed in the Yellow Pages.

It's also worth investigating outlets for special tools that can save both time and money on specific jobs. Here are some of the handiest gadgets to consider:

* Cross-shaft wrench (about $10): Provides extra leverage for easier loosening and removal of stubborn lug nuts. A good alternative is a length of metal pipe - about 18 inches long - that can be slipped over the lug wrench supplied with your car.

* Jack stand (about $6): A safety device that keeps the car from falling to the ground if the jack is removed or faulty. Most jobs require two jack stands for safety.

* Hydraulic jack (about $50): A special heavy-duty jack that can raise the entire front or back of a car in seconds for easier placement of the jack stands.

* Magnetic pickup-tool (about $2): This simple ''magnet on a long shaft'' helps retrieve metal objects, such as nuts and bolts, that fall down in the engine or out of easy reach.

* Lie-down creeper (about $10): A board on wheels that you can lie on to move in and out from under the car quickly.

* Radiator flushing kit (about $4): Easy-to-install kit eliminates the need to remove drain plugs and permits quicker and more effective flushing of the entire cooling system.

* Rubber mallet (about $7): A type of hammer for replacing wheel covers. It assures a tighter fit with less chance of marring or denting the covers. It also is used for body work, such as aligning parts and pounding out minor body dents.

* Penetrating oil (about $1.75 for an 8-ounce can): Helps to free bolts, screws, and other fasteners which are rusted or frozen in place.

* Oil spout (about $2): Helps you do a cleaner job of adding oil to the engine. In one step, it will open a can of oil and form a handy spout for pouring. Use in conjunction with a plastic or metal funnel (about $1) that slips into the mouth of containers to provide a wider, more convenient opening for pouring.

* Oil filter wrench (about $4): A hand-operated device that clamps around the oil filter to provide a better grip for loosening it.

* Tire valve extensions (about $2 for four): These are added to existing valves so you can inflate the tires without removing the wheel covers.